gitlab-ci: Remove remaining allow_failure attributes

Currently there are a few jobs that we are still allowing to fail:

• *-linux-hadrian (done in !1156 (closed))
• validate-aarch64-linux-deb9
• nightly-aarch64-linux-deb9
• release-x86_64-linux-deb9-dwarf
• validate-x86_64-windows-hadrian (see #16574 (closed))
• validate-x86_64-windows
• release-x86_64-windows
• validate-x86_64-windows
• release-x86_64-windows
• release-i386-windows
• nightly-i386-windows

These should be made robust and the allow_failure attribute removed.